The present invention relates to an apparatus and method to detect field sync signals in a high definition television. More particularly, the invention relates to an apparatus and method to detect field sync signals by correlating input data and a reference value.
As a result of significant effort expended in developing a television having a large screen and high resolution, a high definition television (HDTV) receiver for receiving HDTV signals has been produced in Japan.
In the United States, the Grand Alliance (GA) committee has proposed technical standards for designing a HDTV system. The GA committee has adopted the vestigial side band (VSB) modulation as a GA-HDTV modulation standard, including an 8-VSB standard having eight levels for terrestrial broadcast mode and a 16-VSB standard having sixteen levels for high speed cable mode.
FIG. 1 illustrates the format of a VSB data frame according to the GA-HDTV modulation standard. The VSB data frame has two fields, and each field has one field sync segment and 312 data segments. The field sync segments FIELD SYNC #1 and FIELD SYNC #2 are located in the first segment of each field to indicate the beginning of the field.
Each of the data segments has 4 symbols for segment synchronization and 828 data symbols. The segment synchronization is located at the beginning of each data segment and has a predetermined pattern in which the four sync symbols have signal levels of +5, -5, -5, +5. Each of the data symbols assumes an arbitrary signal level out of the eight possible levels .+-.1, .+-.3, .+-.5 and .+-.7.
FIG. 2 is a drawing for explaining a VSB field sync signal of a GA-HDTV.
As shown in FIG. 2, the field sync segment has 832 symbols. The initial 4 symbols are used for segment synchronization. The segment synchronization is followed by 511 symbols, designated as pseudo number PN511, which are in turn followed by 189 symbols divided into three PN63s. The remaining 128 symbols are used to carry other information.
Here, PN511 is a predetermined signal sequence composed of +5 and -5 levels and is used as a training sequence for use in equalization. The phase of the second PN63 is inverted in each field.
Since a field synchronization indicating the beginning of the field is located in the first segment of each field and has a uniform form, the field sync signals can be detected in the receiver. While the signals may be easily detected, the field sync signals should also be detected with accuracy in order to perform synchronization and decoding in a receiver.